I think what many people overlook (possibly the OP) is the labor component of the equation. We can all search online shops and craigslist and ebay for great deals on the various components required to build a big motor but those parts need to be checked, machined and put together in the proper manner. 40 hours of my time building you a motor should cost you about $200 ($5/hour) because I have no idea what I am doing and I have no business building an engine for myself or anyone else.
Jim or Mike's (or any of the other competent builders on this site) time is easily worth north of $100/hour(for reference the labor rate at your typical crappy automotive dealership is usually $95/hour). Factor in the time to build a motor to the standard a professional adheres to, added to the dyno rental time and additional labor of tuning and you have used up a nice chunk of your $8,500.
I would recommend you scour moparts and this site's classifieds and look for someone who is selling a motor built to roughly the specs you are looking for. You will eventually find one in your price range. Those deals pop up from time to time.
Of course you won't know exactly what you are getting. Therein lies the rub...
The thing about the free market system is that things cost what they cost. If you can't readily find someone to build you a motor to the specification and budget that you desire it likely because you are not willing to spend enough money. In the event that you do find someone substantially cheaper than the prevailing rate there is a risk that you might not be getting the quality you had hoped for.
